An analysis of the strain distribution patterns for recombinant-inbred strains of mice immunized with Type III pneumococcal polysaccharide (SSS-III) showed that (a) at least 3-5 genes influence the capacity of bone marrow-derived precursors of antibody-forming cells (B cells) to make an antibody response, (b) at least 2 genes control the expression of suppressor T cell activity, and (c) at least 3-4 genes govern amplifier T cell function. These autosomal immune response genes act independently and in a complementary manner to produce the effects observed. They are not linked to genes within the major histocompatibility (H-2) or immunoglobulin allotype complex.